Manufacture of a silica-hafnia catalyst for conversion of hydrocarbons



Aug- 1961 c. J. PLANK ET AL 2,996,448

MANUFACTURE OF A SILICA-HAFNIA CATALYST FOR CONVERSION OF HYDROCARBONS Filed Dec. 7, 1959 Gasoline Yield Advantage, Vo|.% (M

O 5 IO I5 20 25 30 Weight Percent HfOz INVENTORS. CharlesJ.P|ank BY Edward J.Rosinsk| ATTORNEY r 2,996,448 MANUFACTURE OF A SHJCA-HAFNIA CATA- LYST FOR CONVERSION OF HYDROCARBONS. Charles J. Plank, Woodbury, and Edward I. Rosinski,

Almonesson, N.".l., assignors to Socony Mobil Oil Company, Inc., a corporation of New York 1 Filed Dec. 7, 1959, Ser. No. 857,713-

12 Claims. (Cl. 208-119) This invention relates to the catalytic conversion of hydrocarbons and to an improved catalyst for effecting said conversion. More particularly, the invention relates to the catalytic cracking of hydrocarbon oils in thejp'resence of a new and improved catalyst. In one embodiment, this invention is concerned with an improved silicahafnia cracking catalyst characterized by unusual selectivity in the conversion of hydrocarbons. .In another em bodiment, the invention is directed to an improved method for preparing silica-hafnia composites of such characteristics useful in catalytic cracking ofheavy petroleum fractions to lighter materials boiling in the gasoline range. As is well known, there are numerous materials, both of natural and synthetic origin which have the ability to catalyze the cracking of hydrocarbons. However, the mere ability to catalyze cracking is' far fromsuficient to aiford a catalyst of commercial significance. Of the presently commercially available cracking catalysts, a syn; thetic silica-alumina composite catalyst is by far the most widely used. While such type catalyst is superior in many ways to the earlier employed clay catalysts and is fairly satisfactory it is subject to improvement, particularly as regard to the selectivity desirable in a modern cracking catalyst. i The present invention affords a commercially attractive silica-hafnia catalyst characterized by outstanding seQ lectivity in the conversion of hydrocarbons. The improvement arises from the method of manufacture which comprises a particular combination of procedural steps including the reaction of a water-soluble hafnium compound and a silicate in such proportions as to yield a gelable hydrosol having a hafnia content,'on a dry basis, of between about 1 and about 30 percent by weight and a pH in'excess of 6, permitting the resulting sol to set forming a silica-hafnia gel, reducing the pH of said gel to below 5 and activating the same by maintaining the gel under such conditions of reduced pI-I while incontact with an aqueous medium at a temperature in the approximate range of 150 to 220 F. for at leastv about 1 hour under conditions of substantiallyatmospheric pressure.

After activation in aqueous medium, zeolitic impurities, if any, are removed from the gel and the latter is washed free of water-soluble matter, dried and calcined. In the foregoing procedure, it has been found that the activation step of treating the silica-hafnia gel in an aqueous medium at the specified conditions and the control of pH during gelation and such activation step are essential in achieving the unusually effective selectivity characterizing the present silica-hafnia catalyst. It has further been found, in accordance with the present invention, that not onlyis the activation step essential, but that also the conditions required during this step to obtain the desired 4 2,996,448 Patented Au 15, 19st treatment involving the use of an aqueous medium is; above about F. and preferably above F. and generally does not exceed 220 F. The time required foractivation is generally at least 1 hour and may ex: tend up to 72 hours or longer. Preferably, the' activa tion period is at least 2 hours and usually within the approximate range of 2 to 48 hours. The intermediate hydrogel state obtained in preparation of present catalysts is to be distinguished fro'rn'a" gelatinous precipitate. True all-embracing hydrogels cc: cupy the entire volume'of the solution from which they are formed and possess a definitely rigid structure. When fractured, a true hydrogel shows a 'conchoidal fracture as compared to an irregular ragged edge fraction as obtained inthe case of gelatinous precipitates. The latter occupy only a part of the volume of the solution from which they are formed and have no rigidity of structure. In addition, hydrogels can generally be more easily washed free of soluble impurities due to the tendency of gelatinousprecipitates to peptize on washing. A distinct and further advantage of hydrogels is that due to their rigid structure, they can be formed into high quality spheroidal particles. The hafnium compound employed in the present proc-' ess is a water-soluble compoundand suitably a water soluble mineral acid salt of hafnium such as for example, hafnium nitrate, hafnium sulfate and hafnium oxychloride. Of this group, hafnium sulfate is accorded preference. This compound is readily prepared by dissolving pure hafniumoxide in sulfuric acid. p The silicate reactant is generally an alkali metal silicate and particularly sodium silicate, although silicates of the other alkali metals, such as, for example, potassium sil icate might likewise be employed. An organic silicate ester, for example ethyl ortho silicate, may also be em ployed, as the source of silica.

The solutions of zirconium compound and silicate reactant are intimately mixed in such proportions as to yield a gelable solhaving ahafnia content, on a dry basis, of between about 1 and about 30 and preferably between about 2 and about 25 percent by weight and a pH of above 6 and generally not exceeding about 11. Preferably, the pH of the hydrosol is within the approximaterange of 6.5 to 9.5. 1

The resulting product is a hydrosol of silica and hafnia characterizedby an inherent capacity to set to a hydrogel upon lapse of a suitable interval of time, extending from a few seconds up to several hours depending on pH, temperature and solids concentration, without addition to or subtraction from the hydrosol of any substance. By following the teachings .of this invention, the time of gelation can be very rapid, i.e. less than 20 seconds which permits the gel to be prepared directly 'inthe form of spheroidal particles resulting in a product of improved physical properties and in definite economic advantages in the manufacture of the catalyst. In addition to affording rapid gelation, the high pH of gel formation has been found to give rise to a more selective catalyst as compared with a comparable gel in which'the pH of formation is below 6.

The silica-hafnia hydrogel so obtained, is thereafter treated to reduce the pH thereof to below 5 and preferably less than 3.5 but greater than 1. Toaccomplish such purpose, the hydrogel is contacted with an acidic fluid substantially immediately after formation. While the lapse of a short interval of time is permissible, it is generally desirable to reduce the pH of the silica-hafnia hydrogel immediately upon formation to less than 5. Maintaining the hydrogel under conditions of pH at which formation is effected for a considerable period of time was found to be detrimental to the selectivity of the finished catalyst. Generally, the hydrogel is contacted is EXAMPLE 2" A silica-hafnia catalyst was ing reactants:

Solution A which consisted of 2800 cc. of diluted N produced from the follow- 6 The resulting gel was cut into cubes and asinExamplel.

EXAMPLE 4 A silica-hafnia catalyst was produced from the follow-C brand sodium silicate containing 0.193 gram SiO /cc. and 5 illg IBaQ'EaIItSI v 1 135 f dilute Sodium hydroxide l ti containing Solution A which consisted of 1852 cc. of dilute .N 025 gram NaOH/ brand sodium silicate solution containing 0.193 gram Solution B hi h consisted of 1200 f SiO /cc. and 448 cc. of dilute sodium hydroxide solution containing 0.25 gram NaOH/ cc. Hf (SO -H SO Solution B which consisted of 1260 cc. of

solution containing 0.05 gram HfO /cc. and 5864 cc. of Hf(SO4)2'HZSO4 I water. I containing 0.05 gram HfO /cc. and 5320 cc. of water, To Solution A, cooled to 40 F., was added Solution B, To Solution B, cooled to 33 F. was added Solution A, cooled to 33 F., while agitating vigorously. The resultcooled to 40 F., while agitating vigorously. The resulting hydrosol had a pHof 8.2 and contained 14 percent ing hydrosol had a pH of 8.2 and contained 21 percent weight Hf0 on a finished basis. Gelation to a firm weight HfO on a finished basis. Gelation to a firm hydrogel occurred in about 15 seconds. hydrogel occurred in about 15 seconds. p The resulting gel was cut into cubes and processed as The resulting gel was cut into cubes and processed as in in Example 1. Example 1.

EXAMPLE 3 Cracking characteristics of the above catalysts of Examples 1-4 were determined upon subjecting each of the This errample was use d to compare preparation methods catalysts to the CAT-C test. In this test, a wide-range y formms acfivatmgfihe gel at '1 P The 9 Mid-Continent gas oil, boiling initially from 450 F. to tlolls P 1n y p l We're as follows: n 95 percent at 950 F. is passed over the catalyst sample sohmon A e? of 2800 of (mute N at a standard set of conditions involving a liquid hourly sPdlum S11 1cate coPtammg 0'193 gmm 5102/ space velocity of 2, a catalyst to oil ratio of 3 and a B Whlch conslsted of 1200 of temperature of 900 F. To observe selectivity differences Hf so lndependent of the conversion level of the indivrdual V 2 i srhca-hafma catalyst samples, each catalyst 1s compared containing 0.05 gram HfO /cc., 7.2 cc. of H (50 to a standard commercial silica-alumina cracking catalyst weight percent aqueous solution) and 6000 cc. of water} containing about 10 weight percent alumina and weight To Solution B was added Solution A while agitating percent silica, giving the same conversion as the appro vigorously. The resulting hydrosol had a pH of 3.6 and priate silica-hafnia catalyst. The results for Examples required 4-5 hours to set to a firm gel. The gel, so ob- 35 1-4 are set forth in the table. In this comparison, each of tained, was allowed to stand at room temperature overthe catalysts were treated with percent steam for 20 night, out into cubes and covered with water in which the hours at atmospheric pressure at 1225 F. before the gel was aged for 24 hours at 200 F. cracking test to bring the activity to a reproducible level.

Table Example 1 2 3 4 Description:

Forming pH 8. 5 8. 2 3.6 8. 2 el 15 sec 15 sec. 4-5 hrs. 15 sec.

H4SO14 H2804 H20 H280; 24 24 24 200 200 200 200 p 2.7 2.4 3.2 2.1 Physical Properties:

Pore Vol., cc./g 0.56 0. 48 0. 38 Density, g./cc.

Particle 1. 01 1.12 1. 28 2.33 2. 42 2.49

0. 60 o. 63 o. 73 0. 66 Steamed 1 0. 66 0. 73 o. 86 0.88 Surface Area, m. /g.:

resh 598 624 609 559 V Steamed 1 338 319 271 31a Composition (analyzed) HfOz, percent wt 6.6 14. 0 14. 0 21.0 Na, percent wt 0.06 0. 05 0.07 0. 03 S0 percent wt 0. 09 0. 09 0.15

CAT-O EVALUATION Steamed Gatalystsz Conversion, Vol. Percent 43. 3 54. 4 53'. 6 51.1 10 RVP Gasoline, V01. Percent. 39.8 47. 1 44. 8 46.5 0 Gasoline, Vol. Percent... 36. 5 44.2 41'. 6 43. 1 Total C4s, Vol. Percent 7. 9 12. 2 12.3 9;! Dry Gas, Wt. Percent 4.9 5. 6 6.4 5.0 Coke, Wt. Percent 1.6 2.5 2.9 2.4 Difierence from Sim-A1203:

10 RVP Gaso., Vol. Percent +3.6 +4.3 +2. 5 +5.6 X504, Vol. Percent -3. 5 -2. 7 -2. 7 4.6 Dry Gas, Wt. Percent 0. 0 1. 0 -0. 12 1.=1 Coke, Wt. Percent -0.44 1.0 0. 47 -06 1 Steamed 20 hours at 1225 F. with steam at atmospheric pressure. 3 Value for Sim-Hi0: catalyst minus value torsion-A at the same conversion.

aQ-QQQQQ 7 Eton the sta e, i is vident that of the slica-hafnia hydrogel at the higher pH and subsequent v reduction in pH during activation treatment has several adyantages over comparable formation of the hydrogel initially "at a low pH. Thus, comparing the resultsof E 2 and 3 which have an identical chemical comtiomit will be seen that the gel time is considerably ned in the case of Example 2 repared initially at a high pH over that of Example 3 prepared at low pH. This permits production of the hydrogel in particulate form directly from the hydroso'l without intermediateformation o f a grass of gel which is subsequently br n u a d in P r e of table ize an hape econdly, the activity of the catalysts, after treatme t, e. the steam stability, is higher for 9 sa l s of Example .2 h n the catalyst of Example i f1Y QQQ 9g Ql ne and less coke is format with the catalyst of 2 in comparison with that of stand: 3.-

Turning to the advantage of silica-hafnia over a commercial silicaralumina cracking c t lyst a h e ses ion, it will be seen that the c ys o Ex mple 1 afforded a +3.6 volume percent yield of gasoline; the catalyst if Ex pie 2, a +4.3 volume percent yield of a 21 ei ht per en less w n he c his-.121 4. a volume Pe c n Y ld f a othe cata s oi Exa p 3, prepa d at an y lo p.121 of 3.6 aftorded a +2 ol m p rcent s asoline more than that obtained by commercial sst lys ht th s hle c nve s n this mo nt of s line 2.. v lume per ent s h n o ai ed an e yst sil i mn e .2 w ic as formed t ly activated in said sol tiona c en on th cr ck g sele tivity of the present catalyst is shown by a comparison at the res t Qt r nn e 1, 2 nd h data r sented graphically the attached drawing wherein s in; Yield tl htas b a ned .over a comm cial silicaa1umina cracking catalyst is plotted against hafnia conteht of the catalyst. The cracking selectivity unexpectedly increased with an increase in hafnia content. This trend is rather unexpected since it is opposite to the results exhibited by silica-alumina and silicazirconia types of cracking catalysts wherein cracking selcctivity decreases with anincrease in metal oxide content oi the catalyst.

It will be understood that the above description is merely illustrative of preferred embodiments of the invention, gt which many variations may be made by .those skilled in the art without departing from the spirit thereof.

. We ciaim:

1. A process tor preparing a catalytic composite of 3, is in; .t line.

. gilica and hatnia whichcomprises reacting a water-sol uble hafnium compound and a silicate to effect formation of a gelable sol consisting essentially of silica and :hafnia characterized by a pH in excess of 6 and a hafnia acontent, on a dry solids basis, of between about 1 and .about 30 percent by Weight, permitting the said sol to set forming a silica-hafnia gel, reducing the pH of said gel to below 5 and maintaining the gel under such conditions'of reduced pH while in contact with an aqueous medium at a temperature in the approximate range of 150 to220" F. fof'a periodof at least about 1 hour under conditions of substantially atmospheric pressure, reafter the gel'free of soluble matter, drying calcining;

2. A process for preparing a catalytic composite of silica and hafnia which comprises reactinga water-solu- {blc hatnium compound and an alkali metal silicate to effect formation ofaa gel-able sol consisting essentially 'o fsilica and hafnia characterized by a pH-in excess of 6 and a hafnia content, on a dry solids basis, of 'beshout 21nd shah- 25. Pate by wealter ti: ting the said sol to set forming a silica-hafnia gel, re-

ducing the pH of said gel below 3.5 and maintaining the gel under such condition of reduced pH while in contact an aqueous medium at a temperature in the approximate range of 150 to 220 F. for at least about 2 hours under conditions of substantially atmospheric pressure, thereafter washing the gel free of solo.- ble matter, drying and calcining.

3. A process for preparing a catalytic composite of silica and hafnia which comprises reacting in aqueous solution, a water-soluble hafnium compound and an alkali metal silicate to effect formation of a 'gelable hy- Q P Q cons st g s nt al of li a d hafnia h a teriezed by a pH in excess of 6 but not greater nd a ha ui content, on a d Solids a s of tween about "1 and about 30 percent by weight, permitting the said hydrosol to set forming a silica-hafnia hydrogel, reducing the pH of said hydrogel to below 5 but in excess of 1 and maintaining the hydrogel under such conditions of r c d p while in contact with an aqueous medium at a temperature in the approximate range of 150 to 220 F. for at least about 1 hour under conditions of substantially atmospheric pressure, therea te w shing the e the Qt solub e m tte d y ng a alcining- A or re a in .a catal c om os e o ili and ha nia which mnin isss reactin a ueo ution a wat r-solubl al o minera and and s lica e to et c t forma ion o a sala hydrosol consisting essentially of silica and hafnia characterized by a pH in excess of .6 and a hafnia content, on a solids basis, of between about 2 and about 25 cemen y weight, p rmit g the i y s vto et t a s l ca hafhia 'hydwgel, re c t p hydhossl to h api mat range of 1 t9 3:5'andn1ai ainiac th 'h d c under h conditions of reduced pI l while in contact with an aqueous a :1 san in at a ton sta r i the approximate mas 175 to 200 'F. for a period of about 2 to about 72 hours under conditions of substantially atmospheric pressure, thereafter washing the gel free of soluble matter, drying and calcining.

5. A process for preparing a catalytic composite of silica and hafnia which comprises reacting in aqueous solution, hafnium sulfate and sodium silicate to eflect formation of a gelable hydrosol consisting essentially of silica and hafnia characterized 'by a pH in excess of 6 but not greater than 11, and a hafnia content, on a solids basis, of between about 2 and about 25 percent by weight, permitting the said hydrosol to set forming a silica hafnia hydrogel, reducing the pH of said hydrlogel to below 5 but in excess of l and maintaining the hydrogel under such conditions of reduced pI-I while in contact with an aqueous acidic medium at a temperature in the approximate range of 175 to 200 for a period of between about 2 and about 72 hours under conditions of substantially atmospheric pressure thereafter washing the gel free of soluble matter, drying and calcining at a temperature between about 800 and about 1800 F.

6, A process for the conversion of hydrocarbons which comprises contacting hydrocarbon vapor at conversion conditions of temperature and pressure with a catalyst consisting essentially of silica and hafnia and having a hafnium content of between about 1 and about 30 percent by weight, prepared by a process which comprises reactin-g ;a water-soluble hafnium compound and a silicate to ettect formation of a gelable sol consisting essentially saidsol to set forming a silica-hafnia gel, reducing the pH of said gel to below 5 and maintaining the gel under such conditions of reduced pH while in contact with a an aqueous medium at a temperature in the approximate range of to 220 F. for a period of at least about 1 hour under conditions of substantially atmospheric pressure thereafter washing the gel free of soluble matter, drying and calcining.

7. A process for the conversion of hydrocarbons which comprises contacting hydrocarbon vapor at conversion conditions of temperature and pressure with a catalyst consisting essentially of silica and hafnia and having a hafnium content of between about 1 and about 30 percent by weight, prepared by a process which comprises reacting in aqueous solution, a water-soluble hafnium compound and an alkali metal silicate to effect formation of a gelable hydrosol consisting essentially of silica and hafnia characterized by a pH in excess of 6 but not greater than 11 and a hafnium content, on a dry solids basis, of between about 1 and about 30 percent by weight, permitting the said hydrosol to set forming a silica-hafnia hydrogel, reducing the pH of said hydrogel to below 5 but in excess of l and maintaining the hydrogel under such conditions of reduced pH while in contact with an aqueous medium at a temperature in the approximate range of 150 to 220 F. for at least about 1 hour under conditions of substantially atmospheric pressure, thereafter washing the gel free of soluble matter, drying and calcining.

8. A process for the conversion of hydrocarbons which comprises contacting hydrocarbon vapor at conversion conditions of temperature and pressure with a catalyst consisting essentially of silica and hafnia having a hafnium content of between about 2 and about 25 percent by Weight, prepared by reacting in aqueous solution, a watersoluble hafnium salt of a mineral acid and sodium silicate to eifect formation of a gelable hydrosol consisting essentially of silica and hafnia characterized by a pH in excess of 6, and a hafnia content, on a dry solids basis, of between about 2 and about 25 percent by Weight, permitting the said hydrosol to set forming a silica hafnia hydrogel, reducing the pH of said hydrogel to within the approximate range of 1 to 3.5 and maintaining the hydrogel under such conditions of reduced pH while in contact with aqueous acidic medium at a temperature within the approximate range of 150 to 220 F. for a period of about 2 to about 72 hours under conditions of substantially atmospheric pressure, thereafter washing the gel free of soluble matter, drying and calcining.

9. A process for cracking a heavy petroleum oil to lighter materials boiling in the range of gasoline which comprises contacting said oil at catalytic cracking conditions with a catalyst consisting essentially of silica and hafnia having a hafnia content of between about 2 and about 25 percent by weight, prepared by reacting in aqueous solution, hafnium sulfate and sodium silicate to effect formation of a gelable hydrosol consisting essentially of silica and hafnia characterized by a pH in excess of 6 but not greater than 11 and a hafnium content, on a dry solids basis, of between about 2 and about 25 percent by weight, permitting the said hydrosol to set forming a silica-hafnia hydrogel, reducing the pH of said hydrogel to below 5 but in excess of l and maintaining the hydrogel under such conditions of reduced pH while in contact with an aqueous acidic medium at a temperature within the approximate range of 175 to 200 F.'for a period 10 of between about 2 and about 72 hours under conditions of substantially atmospheric pressure, thereafter washing the gel free of soluble matter, drying and calcining at a temperature between about 800 and about 1800 F.

10. A hydrocarbon conversion catalyst consisting essentially of silica and hafnia having a hafnium content of between about 1 and about 30 percent, prepared by reacting a water-soluble hafnium compound and a silicate to effect formation of a gelable sol, consisting essentially of silica and hafnia characterized by a pH in excess of 6, and a hafnia content, on a dry solids basis, of between about 1 and about 30 percent by weight, permitting the said sol to set forming a silica hafnia gel, reducing the pH of said gel to below 5 and maintaining the gel under such conditions of reduced ipH while in contact with an aqueous medium at a temperature in the approximate range of to 220 F. for a period of at least about 1 hour under conditions of substantially atmospheric pressure, thereafter washing the gel free of soluble matter,v drying and calcining.

11. A hydrocarbon conversion catalyst consisting essen-- tially of silica and hafnia having a hafnium content of between about 1 and about 30 percent by weight, prepared by reacting in aqueous solution, a water-soluble hafnium compound and an alkali metal silicate to eflect formation of a gelable hydrosol consisting essentially of silica and hafnia characterized by a pH in excess of 6 but not greater than 11, and a hafnia content on a dry solids basis, of between about 1 and about 30 percent by weight, permitting the said hydrosol to set forming a, silica-hafnia hydrogel, reducing the pH of said hydrogel, to below 5 but in excess of 1 and maintaining the hydrogel under such conditions of reduced pH while in contact: with an aqueous medium at a temperature in the approximate range of 150 to 220 F. for at least about 1 hourunder conditions of substantially atmospheric pressure. thereafter washing the gel free of soluble matter, drying;

and calcining.

12. A hydrocarbon conversion catalyst consisting essentially of silica and hafnia having a hafnia content of between about 2 and about 25 percent by weight, prepared by reacting in aqueous solution -a water-soluble:

hafnium salt of a mineral acid and sodium silicate to effect formation of a gelable hydrosol consisting e'ssentially of silica and hafnia characterized by a pH in excess: of 6 and a hafnia content, on a dry solids basis, of between about 2 and about 25 percent by weight, permitting the said hydrosol to set forming a silica-hafnia hydrogel, reducing the pH of said hydrogel to Within the approximate range of 1 to 3.5 and maintaining the hydrogel under such conditions of reduced pH While in contact with an aqueous acidic medium at a temperature within the approximate range of to 200 F. for a period of about 2 to about 72 hours under conditions of substantially atmospheric pressure, thereafter washing the gel free of soluble matter, drying and calcining.

Morreil July 26, 1938 Bates et a1. Jan. 1, 1952 

6. A PROCESS FOR THE CONVERSION OF HYDROCARBONS WHICH COMPRISES CONTACTING HYDROCARBON VAPOR AT CONVERSION CONDITIONS OF TEMPERATURE AND PRESSURE WITH A CATALYST CONSISTING ESSENTIALLY OF SILICA AND HAFNIA AND HAVING A HAFNIUM CONTENT OF BETWEEN ABOUT 1 AND ABOUT 30 PERCENT BY WEIGHT, PREPARED BY A PROCESS WHICH COMPRISES REACTING A WATER-SOLUBLE HAFNIUM COMPOUND AND A SILICATE TO EFFECT FORMATION OF A GELABLE SOL CONSISTING ESSENTIALLY OF SILICA AND HAFNIA CHARACTERIZED BY A PH IN EXCESS OF 6 AND A HAFNIA CONTENT, ON A DRY SOLIDS BASIS, OF BETWEEN 